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4nes4snes/usbdrv/usbdrvasm.S
Raphaël Assénat 6c88641e07 Initial revision
2007-03-25 02:59:30 +00:00

759 lines
26 KiB
ArmAsm
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/* Name: usbdrvasm.S
* Project: AVR USB driver
* Author: Christian Starkjohann
* Creation Date: 2004-12-29
* Tabsize: 4
* Copyright: (c) 2005 by OBJECTIVE DEVELOPMENT Software GmbH
* License: Proprietary, free under certain conditions. See Documentation.
* This Revision: $Id: usbdrvasm.S,v 1.1 2007-03-25 02:59:31 raph Exp $
*/
/*
General Description:
This module implements the assembler part of the USB driver. See usbdrv.h
for a description of the entire driver.
Since almost all of this code is timing critical, don't change unless you
really know what you are doing! Many parts require not only a maximum number
of CPU cycles, but even an exact number of cycles!
*/
#include "iarcompat.h"
#ifndef __IAR_SYSTEMS_ASM__
/* configs for io.h */
# define __SFR_OFFSET 0
# define _VECTOR(N) __vector_ ## N /* io.h does not define this for asm */
# include <avr/io.h> /* for CPU I/O register definitions and vectors */
#endif /* __IAR_SYSTEMS_ASM__ */
#include "usbdrv.h" /* for common defs */
/* register names */
#define x1 r16
#define x2 r17
#define shift r18
#define cnt r19
#define x3 r20
#define x4 r21
/* Some assembler dependent definitions and declarations: */
#ifdef __IAR_SYSTEMS_ASM__
# define nop2 rjmp $+2 /* jump to next instruction */
# define XL r26
# define XH r27
# define YL r28
# define YH r29
# define ZL r30
# define ZH r31
# define lo8(x) LOW(x)
# define hi8(x) ((x)>>8) /* not HIGH to allow XLINK to make a proper range check */
extern usbRxBuf, usbDeviceAddr, usbNewDeviceAddr, usbInputBuf
extern usbCurrentTok, usbRxLen, usbRxToken, usbAppBuf, usbTxLen
extern usbTxBuf, usbMsgLen, usbNakBuf, usbAckBuf, usbTxLen1, usbTxBuf1
public usbCrc16
public usbCrc16Append
# ifndef IVT_BASE_ADDRESS
# define IVT_BASE_ADDRESS 0
# endif
ASEG
ORG INT0_vect + IVT_BASE_ADDRESS
rjmp SIG_INTERRUPT0
RSEG CODE
#else /* __IAR_SYSTEMS_ASM__ */
# define nop2 rjmp .+0 /* jump to next instruction */
.text
.global SIG_INTERRUPT0
.type SIG_INTERRUPT0, @function
.global usbCrc16
.global usbCrc16Append
#endif /* __IAR_SYSTEMS_ASM__ */
SIG_INTERRUPT0:
;Software-receiver engine. Strict timing! Don't change unless you can preserve timing!
;interrupt response time: 4 cycles + insn running = 7 max if interrupts always enabled
;max allowable interrupt latency: 32 cycles -> max 25 cycles interrupt disable
;max stack usage: [ret(2), x1, SREG, x2, cnt, shift, YH, YL, x3, x4] = 11 bytes
usbInterrupt:
;order of registers pushed:
;x1, SREG, x2, cnt, shift, [YH, YL, x3]
push x1 ;2 push only what is necessary to sync with edge ASAP
in x1, SREG ;1
push x1 ;2
;sync byte (D-) pattern LSb to MSb: 01010100 [1 = idle = J, 0 = K]
;sync up with J to K edge during sync pattern -- use fastest possible loops
;first part has no timeout because it waits for IDLE or SE1 (== disconnected)
#if !USB_CFG_SAMPLE_EXACT
ldi x1, 5 ;1 setup a timeout for waitForK
#endif
waitForJ:
sbis USBIN, USBMINUS ;1 wait for D- == 1
rjmp waitForJ ;2
#if USB_CFG_SAMPLE_EXACT
;The following code represents the unrolled loop in the else branch. It
;results in a sampling window of 1/4 bit which meets the spec.
sbis USBIN, USBMINUS
rjmp foundK
sbis USBIN, USBMINUS
rjmp foundK
sbis USBIN, USBMINUS
rjmp foundK
nop
nop2
foundK:
#else
waitForK:
dec x1 ;1
sbic USBIN, USBMINUS ;1 wait for D- == 0
brne waitForK ;2
#endif
;{2, 6} after falling D- edge, average delay: 4 cycles [we want 4 for center sampling]
;we have 1 bit time for setup purposes, then sample again:
push x2 ;2
push cnt ;2
push shift ;2
shortcutEntry:
ldi cnt, 1 ;1 pre-init bit counter (-1 because no dec follows, -1 because 1 bit already sampled)
ldi x2, 1<<USB_CFG_DPLUS_BIT ;1 -> 8 edge sync ended with D- == 0
;now wait until SYNC byte is over. Wait for either 2 bits low (success) or 2 bits high (failure)
waitNoChange:
in x1, USBIN ;1 <-- sample, timing: edge + {2, 6} cycles
eor x2, x1 ;1
sbrc x2, 0 ;1 | 2
ldi cnt, 2 ;1 | 0 cnt = numBits - 1 (because dec follows)
mov x2, x1 ;1
dec cnt ;1
brne waitNoChange ;2 | 1
sbrc x1, USBMINUS ;2
rjmp sofError ;0 two consecutive "1" bits -> framing error
;start reading data, but don't check for bitstuffing because these are the
;first bits. Use the cycles for initialization instead. Note that we read and
;store the binary complement of the data stream because eor results in 1 for
;a change and 0 for no change.
in x1, USBIN ;1 <-- sample bit 0, timing: edge + {3, 7} cycles
eor x2, x1 ;1
ror x2 ;1
ldi shift, 0x7f ;1 The last bit of the sync pattern was a "no change"
ror shift ;1
push YH ;2 -> 7
in x2, USBIN ;1 <-- sample bit 1, timing: edge + {2, 6} cycles
eor x1, x2 ;1
ror x1 ;1
ror shift ;1
push YL ;2
lds YL, usbInputBuf ;2 -> 8
in x1, USBIN ;1 <-- sample bit 2, timing: edge + {2, 6} cycles
eor x2, x1 ;1
ror x2 ;1
ror shift ;1
ldi cnt, USB_BUFSIZE;1
ldi YH, hi8(usbRxBuf);1 assume that usbRxBuf does not cross a page
push x3 ;2 -> 8
in x2, USBIN ;1 <-- sample bit 3, timing: edge + {2, 6} cycles
eor x1, x2 ;1
ror x1 ;1
ror shift ;1
ser x3 ;1
nop ;1
rjmp rxbit4 ;2 -> 8
shortcutToStart: ;{,43} into next frame: max 5.5 sync bits missed
#if !USB_CFG_SAMPLE_EXACT
ldi x1, 5 ;2 setup timeout
#endif
waitForJ1:
sbis USBIN, USBMINUS ;1 wait for D- == 1
rjmp waitForJ1 ;2
#if USB_CFG_SAMPLE_EXACT
;The following code represents the unrolled loop in the else branch. It
;results in a sampling window of 1/4 bit which meets the spec.
sbis USBIN, USBMINUS
rjmp foundK1
sbis USBIN, USBMINUS
rjmp foundK1
sbis USBIN, USBMINUS
rjmp foundK1
nop
nop2
foundK1:
#else
waitForK1:
dec x1 ;1
sbic USBIN, USBMINUS ;1 wait for D- == 0
brne waitForK1 ;2
#endif
pop YH ;2 correct stack alignment
nop2 ;2 delay for the same time as the pushes in the original code
rjmp shortcutEntry ;2
; ################# receiver loop #################
; extra jobs done during bit interval:
; bit 6: se0 check
; bit 7: or, store, clear
; bit 0: recover from delay [SE0 is unreliable here due to bit dribbling in hubs]
; bit 1: se0 check
; bit 2: se0 check
; bit 3: overflow check
; bit 4: se0 check
; bit 5: rjmp
; stuffed* helpers have the functionality of a subroutine, but we can't afford
; the overhead of a call. We therefore need a separate routine for each caller
; which jumps back appropriately.
stuffed5: ;1 for branch taken
in x2, USBIN ;1 <-- sample @ +1
andi x2, USBMASK ;1
breq se0a ;1
andi x3, 0xc0 ;1 (0xff03 >> 2) & 0xff
ori shift, 0xfc ;1
rjmp rxbit6 ;2
stuffed6: ;1 for branch taken
in x1, USBIN ;1 <-- sample @ +1
andi x1, USBMASK ;1
breq se0a ;1
andi x3, 0x81 ;1 (0xff03 >> 1) & 0xff
ori shift, 0xfc ;1
rjmp rxbit7 ;2
; This is somewhat special because it has to compensate for the delay in bit 7
stuffed7: ;1 for branch taken
andi x1, USBMASK ;1 already sampled by caller
breq se0a ;1
mov x2, x1 ;1 ensure correct NRZI sequence [we can save andi x3 here]
ori shift, 0xfc ;1
in x1, USBIN ;1 <-- sample bit 0
rjmp unstuffed7 ;2
stuffed0: ;1 for branch taken
in x1, USBIN ;1 <-- sample @ +1
andi x1, USBMASK ;1
breq se0a ;1
andi x3, 0xfe ;1 (0xff03 >> 7) & 0xff
ori shift, 0xfc ;1
rjmp rxbit1 ;2
;-----------------------------
rxLoop:
brlo stuffed5 ;1
rxbit6:
in x1, USBIN ;1 <-- sample bit 6
andi x1, USBMASK ;1
breq se0a ;1
eor x2, x1 ;1
ror x2 ;1
ror shift ;1
cpi shift, 4 ;1
brlo stuffed6 ;1
rxbit7:
in x2, USBIN ;1 <-- sample bit 7
eor x1, x2 ;1
ror x1 ;1
ror shift ;1
eor x3, shift ;1 x3 is 0 at bit locations we changed, 1 at others
st y+, x3 ;2 the eor above reconstructed modified bits and inverted rx data
ser x3 ;1
rxbit0:
in x1, USBIN ;1 <-- sample bit 0
cpi shift, 4 ;1
brlo stuffed7 ;1
unstuffed7:
eor x2, x1 ;1
ror x2 ;1
ror shift ;1
cpi shift, 4 ;1
brlo stuffed0 ;1
rxbit1:
in x2, USBIN ;1 <-- sample bit 1
andi x2, USBMASK ;1
se0a: ; enlarge jump range to SE0
breq se0 ;1 check for SE0 more often close to start of byte
eor x1, x2 ;1
ror x1 ;1
ror shift ;1
cpi shift, 4 ;1
brlo stuffed1 ;1
rxbit2:
in x1, USBIN ;1 <-- sample bit 2
andi x1, USBMASK ;1
breq se0 ;1
eor x2, x1 ;1
ror x2 ;1
ror shift ;1
cpi shift, 4 ;1
brlo stuffed2 ;1
rxbit3:
in x2, USBIN ;1 <-- sample bit 3
eor x1, x2 ;1
ror x1 ;1
ror shift ;1
dec cnt ;1 check for buffer overflow
breq overflow ;1
cpi shift, 4 ;1
brlo stuffed3 ;1
rxbit4:
in x1, USBIN ;1 <-- sample bit 4
andi x1, USBMASK ;1
breq se0 ;1
eor x2, x1 ;1
ror x2 ;1
ror shift ;1
cpi shift, 4 ;1
brlo stuffed4 ;1
rxbit5:
in x2, USBIN ;1 <-- sample bit 5
eor x1, x2 ;1
ror x1 ;1
ror shift ;1
cpi shift, 4 ;1
rjmp rxLoop ;2
;-----------------------------
stuffed1: ;1 for branch taken
in x2, USBIN ;1 <-- sample @ +1
andi x2, USBMASK ;1
breq se0 ;1
andi x3, 0xfc ;1 (0xff03 >> 6) & 0xff
ori shift, 0xfc ;1
rjmp rxbit2 ;2
stuffed2: ;1 for branch taken
in x1, USBIN ;1 <-- sample @ +1
andi x1, USBMASK ;1
breq se0 ;1
andi x3, 0xf8 ;1 (0xff03 >> 5) & 0xff
ori shift, 0xfc ;1
rjmp rxbit3 ;2
stuffed3: ;1 for branch taken
in x2, USBIN ;1 <-- sample @ +1
andi x2, USBMASK ;1
breq se0 ;1
andi x3, 0xf0 ;1 (0xff03 >> 4) & 0xff
ori shift, 0xfc ;1
rjmp rxbit4 ;2
stuffed4: ;1 for branch taken
in x1, USBIN ;1 <-- sample @ +1
andi x1, USBMASK ;1
breq se0 ;1
andi x3, 0xe0 ;1 (0xff03 >> 3) & 0xff
ori shift, 0xfc ;1
rjmp rxbit5 ;2
;################ end receiver loop ###############
overflow: ; ignore package if buffer overflow
rjmp rxDoReturn ; enlarge jump range
;This is the only non-error exit point for the software receiver loop
;{4, 20} cycles after start of SE0, typically {10, 18} after SE0 start = {-6, 2} from end of SE0
;next sync starts {16,} cycles after SE0 -> worst case start: +4 from next sync start
;we don't check any CRCs here because there is no time left.
se0: ;{-6, 2} from end of SE0 / {,4} into next frame
mov cnt, YL ;1 assume buffer in lower 256 bytes of memory
lds YL, usbInputBuf ;2 reposition to buffer start
sub cnt, YL ;1 length of message
ldi x1, 1<<USB_INTR_PENDING_BIT ;1
cpi cnt, 3 ;1
out USB_INTR_PENDING, x1;1 clear pending intr and check flag later. SE0 must be over. {,10} into next frame
brlo rxDoReturn ;1 ensure valid packet size, ignore others
ld x1, y ;2 PID
ldd x2, y+1 ;2 ADDR + 1 bit endpoint number
mov x3, x2 ;1 store for endpoint number
andi x2, 0x7f ;1 mask endpoint number bit
lds shift, usbDeviceAddr;2
cpi x1, USBPID_SETUP ;1
breq isSetupOrOut ;2 -> 19 = {13, 21} from SE0 end
cpi x1, USBPID_OUT ;1
breq isSetupOrOut ;2 -> 22 = {16, 24} from SE0 end / {,24} into next frame
cpi x1, USBPID_IN ;1
breq handleIn ;1
#define USB_DATA_MASK ~(USBPID_DATA0 ^ USBPID_DATA1)
andi x1, USB_DATA_MASK ;1
cpi x1, USBPID_DATA0 & USB_DATA_MASK ;1
brne rxDoReturn ;1 not a data PID -- ignore
isData:
lds x2, usbCurrentTok ;2
tst x2 ;1
breq rxDoReturn ;1 for other device or spontaneous data -- ignore
lds x1, usbRxLen ;2
cpi x1, 0 ;1
brne sendNakAndReti ;1 no buffer space available / {30, 38} from SE0 end
; 2006-03-11: The following two lines fix a problem where the device was not
; recognized if usbPoll() was called less frequently than once every 4 ms.
cpi cnt, 4 ;1 zero sized data packets are status phase only -- ignore and ack
brmi sendAckAndReti ;1 keep rx buffer clean -- we must not NAK next SETUP
sts usbRxLen, cnt ;2 store received data, swap buffers
sts usbRxToken, x2 ;2
lds x1, usbAppBuf ;2
sts usbAppBuf, YL ;2
sts usbInputBuf, x1 ;2 buffers now swapped
rjmp sendAckAndReti ;2 -> {43, 51} from SE0 end
handleIn: ; {18, 26} from SE0 end
cp x2, shift ;1 shift contains our device addr
brne rxDoReturn ;1 other device
#if USB_CFG_HAVE_INTRIN_ENDPOINT
sbrc x3, 7 ;2 x3 contains addr + endpoint
rjmp handleIn1 ;0
#endif
lds cnt, usbTxLen ;2
cpi cnt, -1 ;1
breq sendNakAndReti ;1 -> {27, 35} from SE0 end
ldi x1, -1 ;1
sts usbTxLen, x1 ;2 buffer is now free
ldi YL, lo8(usbTxBuf) ;1
ldi YH, hi8(usbTxBuf) ;1
rjmp usbSendAndReti ;2 -> {34, 43} from SE0 end
; Comment about when to set usbTxLen to -1:
; We should set it back to -1 when we receive the ACK from the host. This would
; be simple to implement: One static variable which stores whether the last
; tx was for endpoint 0 or 1 and a compare in the receiver to distinguish the
; ACK. However, we set it back to -1 immediately when we send the package,
; assuming that no error occurs and the host sends an ACK. We save one byte
; RAM this way and avoid potential problems with endless retries. The rest of
; the driver assumes error-free transfers anyway.
otherOutOrSetup:
clr x1
sts usbCurrentTok, x1
rxDoReturn:
pop x3 ;2
pop YL ;2
pop YH ;2
rjmp sofError ;2
isSetupOrOut: ; we must be fast here -- a data package may follow / {,24} into next frame
cp x2, shift ;1 shift contains our device addr
brne otherOutOrSetup ;1 other device -- ignore
sts usbCurrentTok, x1 ;2
#if 0 /* we implement only one rx endpoint */
sts usbRxEndp, x3 ;2 only stored if we may have to distinguish endpoints
#endif
;A transmission can still have data in the output buffer while we receive a
;SETUP package with an IN phase. To avoid that the old data is sent as a reply,
;we abort transmission. ### This mechanism assumes that NO OUT OR SETUP package
;is ever sent to endpoint 1. We would abort transmission for endpoint 0
;in this case.
ldi x1, -1 ;1
sts usbMsgLen, x1 ;2
sts usbTxLen, x1 ;2 abort transmission
pop x3 ;2
pop YL ;2
in x1, USB_INTR_PENDING;1
sbrc x1, USB_INTR_PENDING_BIT;1 check whether data is already arriving {,41} into next frame
rjmp shortcutToStart ;2 save the pops and pushes -- a new interrupt is aready pending
;If the jump above was not taken, we can be at {,2} into the next frame here
pop YH ;2
txDoReturn:
sofError: ; error in start of frame -- ignore frame
ldi x1, 1<<USB_INTR_PENDING_BIT;1 many int0 events occurred during our processing -- clear pending flag
out USB_INTR_PENDING, x1;1
pop shift ;2
pop cnt ;2
pop x2 ;2
pop x1 ;2
out SREG, x1 ;1
pop x1 ;2
reti ;4 -> {,21} into next frame -> up to 3 sync bits missed
sendNakAndReti: ; 21 cycles until SOP
ldi YL, lo8(usbNakBuf) ;1
ldi YH, hi8(usbNakBuf) ;1
rjmp usbSendToken ;2
sendAckAndReti: ; 19 cycles until SOP
ldi YL, lo8(usbAckBuf) ;1
ldi YH, hi8(usbAckBuf) ;1
usbSendToken:
ldi cnt, 2 ;1
;;;;rjmp usbSendAndReti fallthrough
; USB spec says:
; idle = J
; J = (D+ = 0), (D- = 1) or USBOUT = 0x01
; K = (D+ = 1), (D- = 0) or USBOUT = 0x02
; Spec allows 7.5 bit times from EOP to SOP for replies (= 60 cycles)
;usbSend:
;pointer to data in 'Y'
;number of bytes in 'cnt' -- including sync byte
;uses: x1...x4, shift, cnt, Y
usbSendAndReti: ; SOP starts 16 cycles after call
push x4 ;2
in x1, USBOUT ;1
cbr x1, USBMASK ;1 mask out data bits
ori x1, USBIDLE ;1 idle
out USBOUT, x1 ;1 prepare idle state
ldi x4, USBMASK ;1 exor mask
in x2, USBDDR ;1
ori x2, USBMASK ;1 set both pins to output
out USBDDR, x2 ;1 <-- acquire bus now
; need not init x2 (bitstuff history) because sync starts with 0
ldi shift, 0x80 ;1 sync byte is first byte sent
rjmp txLoop ;2 -> 13 + 3 = 16 cycles until SOP
#if USB_CFG_HAVE_INTRIN_ENDPOINT /* placed here due to relative jump range */
handleIn1:
lds cnt, usbTxLen1
cpi cnt, -1
breq sendNakAndReti
ldi x1, -1
sts usbTxLen1, x1
ldi YL, lo8(usbTxBuf1)
ldi YH, hi8(usbTxBuf1)
rjmp usbSendAndReti
#endif
bitstuff0: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
out USBOUT, x1 ;1 <-- out
rjmp didStuff0 ;2 branch back 2 cycles earlier
bitstuff1: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
sec ;1 set carry so that brsh will not jump
out USBOUT, x1 ;1 <-- out
rjmp didStuff1 ;2 jump back 1 cycle earler
bitstuff2: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
rjmp didStuff2 ;2 jump back 3 cycles earlier and do out
bitstuff3: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
rjmp didStuff3 ;2 jump back earlier
txLoop:
sbrs shift, 0 ;1
eor x1, x4 ;1
out USBOUT, x1 ;1 <-- out
ror shift ;1
ror x2 ;1
didStuff0:
cpi x2, 0xfc ;1
brsh bitstuff0 ;1
sbrs shift, 0 ;1
eor x1, x4 ;1
ror shift ;1
out USBOUT, x1 ;1 <-- out
ror x2 ;1
cpi x2, 0xfc ;1
didStuff1:
brsh bitstuff1 ;1
sbrs shift, 0 ;1
eor x1, x4 ;1
ror shift ;1
ror x2 ;1
didStuff2:
out USBOUT, x1 ;1 <-- out
cpi x2, 0xfc ;1
brsh bitstuff2 ;1
sbrs shift, 0 ;1
eor x1, x4 ;1
ror shift ;1
ror x2 ;1
didStuff3:
cpi x2, 0xfc ;1
out USBOUT, x1 ;1 <-- out
brsh bitstuff3 ;1
nop2 ;2
ld x3, y+ ;2
sbrs shift, 0 ;1
eor x1, x4 ;1
out USBOUT, x1 ;1 <-- out
ror shift ;1
ror x2 ;1
didStuff4:
cpi x2, 0xfc ;1
brsh bitstuff4 ;1
sbrs shift, 0 ;1
eor x1, x4 ;1
ror shift ;1
out USBOUT, x1 ;1 <-- out
ror x2 ;1
cpi x2, 0xfc ;1
didStuff5:
brsh bitstuff5 ;1
sbrs shift, 0 ;1
eor x1, x4 ;1
ror shift ;1
ror x2 ;1
didStuff6:
out USBOUT, x1 ;1 <-- out
cpi x2, 0xfc ;1
brsh bitstuff6 ;1
sbrs shift, 0 ;1
eor x1, x4 ;1
ror shift ;1
ror x2 ;1
didStuff7:
cpi x2, 0xfc ;1
out USBOUT, x1 ;1 <-- out
brsh bitstuff7 ;1
mov shift, x3 ;1
dec cnt ;1
brne txLoop ;2 | 1
cbr x1, USBMASK ;1 prepare SE0 [spec says EOP may be 15 to 18 cycles]
pop x4 ;2
out USBOUT, x1 ;1 <-- out SE0 -- from now 2 bits = 16 cycles until bus idle
ldi cnt, 2 ;| takes cnt * 3 cycles
se0Delay: ;|
dec cnt ;|
brne se0Delay ;| -> 2 * 3 = 6 cycles
;2006-03-06: moved transfer of new address to usbDeviceAddr from C-Code to asm:
lds x2, usbNewDeviceAddr ;2
subi YL, lo8(usbNakBuf + 2) ;1
sbci YH, hi8(usbNakBuf + 2) ;1
breq skipAddrAssign ;2
sts usbDeviceAddr, x2 ;0 if not skipped: SE0 is one cycle longer
skipAddrAssign:
;end of usbDeviceAddress transfer
ori x1, USBIDLE ;1
in x2, USBDDR ;1
cbr x2, USBMASK ;1 set both pins to input
out USBOUT, x1 ;1 <-- out J (idle) -- end of SE0 (EOP signal)
cbr x1, USBMASK ;1 configure no pullup on both pins
pop x3 ;2
pop YL ;2
out USBDDR, x2 ;1 <-- release bus now
out USBOUT, x1 ;1 set pullup state
pop YH ;2
rjmp txDoReturn ;2 [we want to jump to rxDoReturn, but this saves cycles]
bitstuff4: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
out USBOUT, x1 ;1 <-- out
rjmp didStuff4 ;2 jump back 2 cycles earlier
bitstuff5: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
sec ;1 set carry so that brsh is not taken
out USBOUT, x1 ;1 <-- out
rjmp didStuff5 ;2 jump back 1 cycle earlier
bitstuff6: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
rjmp didStuff6 ;2 jump back 3 cycles earlier and do out there
bitstuff7: ;1 (for branch taken)
eor x1, x4 ;1
ldi x2, 0 ;1
rjmp didStuff7 ;2 jump back 4 cycles earlier
; ######################## utility functions ########################
#ifdef __IAR_SYSTEMS_ASM__
/* Register assignments for usbCrc16 on IAR cc */
/* Calling conventions on IAR:
* First parameter passed in r16/r17, second in r18/r19 and so on.
* Callee must preserve r4-r15, r24-r29 (r28/r29 is frame pointer)
* Result is passed in r16/r17
*/
RTMODEL "__rt_version", "3"
/* The line above will generate an error if cc calling conventions change.
* The value "3" above is valid for IAR 4.10B/W32
*/
# define argLen r18 /* argument 2 */
# define argPtrL r16 /* argument 1 */
# define argPtrH r17 /* argument 1 */
# define resCrcL r16 /* result */
# define resCrcH r17 /* result */
# define ptrL ZL
# define ptrH ZH
# define ptr Z
# define byte r22
# define bitCnt r19
# define polyL r20
# define polyH r21
# define scratch r23
#else /* __IAR_SYSTEMS_ASM__ */
/* Register assignments for usbCrc16 on gcc */
/* Calling conventions on gcc:
* First parameter passed in r24/r25, second in r22/23 and so on.
* Callee must preserve r1-r17, r28/r29
* Result is passed in r24/r25
*/
# define argLen r22 /* argument 2 */
# define argPtrL r24 /* argument 1 */
# define argPtrH r25 /* argument 1 */
# define resCrcL r24 /* result */
# define resCrcH r25 /* result */
# define ptrL XL
# define ptrH XH
# define ptr x
# define byte r18
# define bitCnt r19
# define polyL r20
# define polyH r21
# define scratch r23
#endif
; extern unsigned usbCrc16(unsigned char *data, unsigned char len);
; data: r24/25
; len: r22
; temp variables:
; r18: data byte
; r19: bit counter
; r20/21: polynomial
; r23: scratch
; r24/25: crc-sum
; r26/27=X: ptr
usbCrc16:
mov ptrL, argPtrL
mov ptrH, argPtrH
ldi resCrcL, 0xff
ldi resCrcH, 0xff
ldi polyL, lo8(0xa001)
ldi polyH, hi8(0xa001)
crcByteLoop:
subi argLen, 1
brcs crcReady
ld byte, ptr+
ldi bitCnt, 8
crcBitLoop:
mov scratch, byte
eor scratch, resCrcL
lsr resCrcH
ror resCrcL
lsr byte
sbrs scratch, 0
rjmp crcNoXor
eor resCrcL, polyL
eor resCrcH, polyH
crcNoXor:
dec bitCnt
brne crcBitLoop
rjmp crcByteLoop
crcReady:
com resCrcL
com resCrcH
ret
; extern unsigned usbCrc16Append(unsigned char *data, unsigned char len);
usbCrc16Append:
rcall usbCrc16
st ptr+, resCrcL
st ptr+, resCrcH
ret
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